For the first time in fifteen or more years, Redmond faces a genuine challenge to its Windows desktop monopoly. The threat isn't coming from Linux or from Mac OS X or from any other operating system. It's coming from a whole new computing concept: the "post-PC." The worry is that upstart tablets threaten to drive the computer out of the home, taking the Windows operating system with it.

It's not just Microsoft that's facing a tumultuous revolution, of course—the PC as a platform, as a concept, is equally under attack. But the biggest loser from this new world order will surely be Microsoft. Hardware makers can just switch to making new hardware, but Microsoft needs that hardware to run Microsoft software, and the company has been consistently unable to crack the tablet market.

Microsoft is no newcomer to the tablet market; in fact, the company has been in the tablet market longer than almost anyone else. But success in this market has been hard to come by. Microsoft's hope, the PC's great hope, is Windows 8. With Windows 8, Microsoft needs to build not just a Windows that PC users want to use; it needs to build a Windows that can succeed in the post-PC world.